The present disclosure relates generally to implantable physiological shunt systems and related fluid flow control devices as well as accessories for use therewith. More specifically, the present disclosure provides devices, systems and methods relating to implantable medical fluid flow control devices, rotors and magnets with increased resistance to inadvertent setting changes. The present disclosure also provides devices, systems and methods relating implantable medical fluid flow control devices, rotors and magnets which provide improved magnetic coupling to fluid flow control device accessories such as adjustment tools.
Generally, a fluid flow control device includes a one-way control valve for controlling the flow of cerebrospinal (CSF) fluid out of a brain ventricle and preventing backflow of fluid into the brain ventricle. One example of a fluid flow control device is disclosed, for example, in U.S. Pat. No. 5,637,083 entitled, “Implantable Adjustable Fluid Flow Control Valve”, incorporated by reference herein in its entirety. Hydrocephalus, a neurological condition which may affect infants, children and adults, results from an undesirable accumulation of fluids, such as CSF, within the ventricles, or cavities, of the brain and which accumulation may exert extreme pressure with brain and in infants, skull deforming forces. Treatment of hydrocephalus often involves draining CSF away from the brain ventricles utilizing a drainage or shunt system including one or more catheters and a shunt valve which may generally be described as a fluid flow control device. The shunt valve, or fluid flow control device, may have a variety of configurations and may be adjustable in that the valve mechanism of the device may be set to a threshold pressure level at which fluid may be allowed to begin to flow through the valve and drain away from the brain. Fluid flow control devices may be subcutaneously implantable and percutaneously adjustable. Flow control devices may have a number of pressure settings and may be adjustable to the various pressure settings via external magnetic adjustment tools. Some fluid flow control devices are magnetic in that the devices include a magnetic rotor or rotor assembly which interacts with a valve mechanism and an adjustment mechanism to selectively adjust a valve opening pressure. The magnetic rotor or rotor assembly may magnetically couple with an external magnetic adjustment tool or tools. Magnetized rotors often include a single magnet or dual magnets arranged or configured to have aligned horizontal polarity. The magnetic adjustment tools are designed to externally (i.e., external to a patient) couple to a rotor magnet of a fluid flow control device implanted in a patient such that upon coupling, the rotor may be deliberately rotated to thereby adjust the pressure setting of the device non-invasively. Adjustment tools can include magnets which may be placed in line with the rotor magnet or magnets in order to couple to and drive the rotor externally, or through the tissue, after the valve is implanted. Typically, an adjustment tool is placed externally, for example, on the patient's head and in proximity to the implanted device. In this manner, it is possible to set the valve rotor into a desired position in a non-invasive manner.
A rotor or rotor assembly having a single magnet or dual magnets with aligned horizontal polarity may cause the magnetic rotor to be susceptible to movement or inadvertent setting adjustment by a strong nearby magnetic field since the internal magnetic elements arranged in this manner may tend to align with the external field. A magnetic rotor might thus be unintentionally adjusted when in the presence of a strong external magnetic field such as encountered in a magnetic resonance imaging (MRI) procedure, for example an MRI field of up to 3.0 Tesla. Unintentional adjustment can result in the rotor moving to a position whereby the pressure setting of the fluid flow control device is other than optimal for the particular patient. Depending upon how a valve or device (and thereby the magnetic rotor) enters the MRI, the magnetic field of the MRI equipment may work to turn (i.e., rotate) the rotor to a new setting, or, if the valve enters the MRI equipment at a 90 degree angle to the MRI magnetic field, the MRI field may work to flip (tilt) the rotor. Potential unintended adjustment may therefore require checking and/or re-adjustment via the external accessories and/or adjustment tools each time a patient is or has been in the presence of a strong external magnetic field. Therefore, the need exists for a fluid flow control device, rotor, and/or magnet which provides increased resistance to inadvertent setting changes.
Intentional adjustment, verification and indication of fluid flow control device or valve pressure settings may be accomplished via external tools and/or accessories including, for example, locator, indicator and/or adjustment tools. As described above, an adjustment tool may include a magnet or magnets for coupling to and rotating an implanted rotor assembly thereby setting a device or valve pressure threshold. However, since during use the adjustment tool is located at a distance from the implanted valve and is external to the patient, device components and/or tissue between the adjustment tool magnets and valve magnet or magnets may interfere with the magnetic coupling of the two. This interference can result in a decreased magnetic field strength making intentional adjustment of pressure settings more challenging. Therefore it may be desirable to improve or increase the magnetic coupling or magnetic field strength between an implanted fluid flow control device and related external magnetically coupleable accessories.
U.S. Pat. No. 5,643,194 to Negre describes a subcutaneous valve and device for externally setting it. Negre describes two micromagnets mounted in a rotor and locking means for locking the rotor in predetermined positions. The locking means described require internal device parts to move linearly to engage mechanical stops for locking the rotor in place. It may be desirable to avoid this type of mechanism since moving mechanical parts tend to decrease life of a product and increase mechanical wear. In addition, it is often desirable to design components which utilize or take up as little space as possible in implantable medical devices such as fluid flow control devices. The locking mechanism described by Negre may undesirably or unnecessarily utilize space for several reasons not the least of which may include by virtue of requiring the particular moving parts disclosed. Another disadvantage of this design is that biological debris is more likely to undesirably interfere with or jam the movable parts.
U.S. Patent Application Publication No. 2012/0046595 to Wilson et. al. describes an implantable adjustable valve. Wilson et. al. describe a rotor for a valve unit where rotor magnets may have axes of magnetization arranged to lie at an angle relative to an axis of rotation of the rotor purportedly to achieve improved interaction with an indicator or adjustment tool. Wilson et. al. describes the angled axes of magnetization are achieved by physically tilting the magnets within the valve assembly such that the magnets themselves lie in a plane angled with respect to a flat or horizontal planar surface of the valve. Physically tilting or angling the magnets in the manner described by Wilson et. al. may also undesirably utilize space within a device.